Punching shear behaviour of geopolymer concrete two-way slabs reinforced by FRP bars under monotonic and cyclic loadings

This study examines the punching shear and deflection performance of 16 Geopolymer concrete (GC) two-way slabs subjected to monotonic and cyclic loading by considering the reinforcement material, percentage of reinforcement, type of concrete and the concrete grade. The tested specimens indicated that the crack patterns at the failure and failure modes were almost similar regardless of the type of reinforcement or their ratio. Moreover, the slabs reinforced by fibre-reinforced polymer (FRP) bars exhibited a lower punching capacity than those strengthened by steel bars, even for similar reinforcement ratios. In addition, the results showed that upon increasing the concrete strength and reinforcement ratio, a higher punching shear capacity and lower deflections were obtained under cyclic and monotonic loading. In addition, the punching shear performance of GC slabs was found to be better than that of ordinary concrete (OC), even though both were reinforced by the basalt FRP (BFRP) bar. However, the ultimate load capacity of the slabs was reduced as a result of cyclic loading according to the capacity of the same specimen, resulting from static loading. However, the reduction is very low for slabs reinforced with FRP slabs. Further, the slabs reinforced by FRP had a better fatigue performance compared with slabs reinforced by steel bars with respect to cyclic loading. The results of the tests were also used to evaluate the accuracy of the available punching shear capacity equations.

Punching Shear Strength Prediction for Reinforced Concrete Flat Slabs without Shear Reinforcement

Failure of flat slabs usually occurs by punching shear mode. Current structural codes provide an experience-based design provision for punching shear strength which is often associated with high bias and variance. This paper investigates the effect of adding a horizontal reinforcement mesh at the top of the slab-column connection zone on punching the shear strength of flat slabs. A new equation considering the effect of adding this mesh was proposed to determine the punching shear strength. The proposed equation is based on the Critical Shear Crack Theory combined with the analysis of results extracted from previous experimental and theoretical studies. Moreover, the equation of load-rotation curves for different steel ratios together with the failure criterion curves were evaluated to get the design points. The investigated parameters were the slab thicknesses and dimensions, concrete strengths, size of the supporting column, and steel ratios. The model was validated using a new set of specimens and the results were also compared with the predictions of different international design codes (ACI318, BS8110, AS3600, and Eurocode 2). Statistical analysis provides that the proposed equation can predict the punching shear strength with a level of high accuracy (Mean Square Error =2.5%, Standard Deviation =0.104, Mean=1.0) and over a wide range of reinforcement ratios and compressive strengths of concrete. Most of the predictions were conservative with an underestimation rate of 12%. Doi: 10.28991/CEJ-2022-08-01-013 Full Text: PDF

Punching Shear Failure Regulation of Reinforced Concrete Beams Subjected to Close-in Explosion

Aiming at the damage effect of reinforced concrete beams subjected to close-in explosion, numerical simulation and dimensional analysis are carried out to study the damage of beams under close-in explosion with spherical charge. The damage characteristics of beams were obtained by the methods of AUTODYN and DYNA. Using dimensional analysis, the relationship between the damage characteristics of reinforced concrete beams and the stand-off distance is deduced. The empirical equation of the beam punching shear failure characteristics is fitted on the basis of numerical simulation. The results show that the simulation method is more efficient than the fluid-solid coupling calculation; the proposed empirical equation is in good agreement with the experimental results. The relationship between failure width and the stand-off distance obtained by the fitting and the modelling method have reference value for the research on the damage effect of reinforced concrete beams.